This invention relates in general to an electrostatographic imaging member comprised of two separate charge transport layers and a photogenerating layer; and more specifically,
(1) a first charge transport layer comprised of a charge transport component and a resin binder; and thereover and in contact with the first layer,
(2) a second top charge transport layer comprised of a charge transport component, a resin binder and a hindered phenol dopant, and wherein in embodiments the second charge transport layer is applied from a mixture of resin binder, especially a polycarbonate, like poly(4,4′-diphenyl)-1,1′-cyclohexane carbonate, PCZ, and a hindered phenol contained in a solvent which does not substantially dissolve components, especially the resin binder of the first charge transport layer, and cause undesirable migration of the hindered phenol through the first charge transport layer, and in some instances through the charge generating layer. Solvents such as, for example, tetrahydrofuran, trichloroethylene, trichloroethane, 2,4-dichlorobenzene, chloroform and the like may be used in the second charge transport layer. A number of charge transport molecules oxidize to form conductive species upon exposure to corona effluents emitted from machine charging devices. With a single charge transport layer, the undesirable oxidation products of N,N′-diphenyl-N,N′-bis(alkylphenyl)-1,1-biphenyl-4,4′-diamine reside on the imaging member surface. These charged species allow the charged image to diffuse or migrate laterally. These species may also migrate from the charge transport layer to the photogenerating layer resulting in image degradation.
Advantages associated with the imaging members of the present invention in embodiments thereof include, for example, the avoidance of the formation of conductive by-products, the undesirable migration of a hindered phenol to the photogenerating layer, thereby avoiding imaging member instability, such as, electrical performance degradation, and undesirable electrical characteristics especially on long term cycling of the member; coating of two transport layers in separate passes to, for example, minimize transport layer thickness variations, which variations can cause image defects referred to as rain drops; minimizing and in embodiments, avoiding an increase in the lateral surface conductivity of the member which in turn can cause image degradation, referred to as lateral conductivity migration (LCM); and in embodiments the elimination of charge transport component oxidation is achieved wherein selected amounts for example, from about 3 to about 20 percent by weight of a hindered phenol, tetrakis[methylene(3,5-di-tert-butyl-4-hydroxy hydrocinnamate)]methaneIRGANOX®-1010 is added to a solution containing a resin binder and a charge transport component dissolved in a solvent other than for example, a solvent that will dissolve the resin binder of the first charge transport layer such as methylene chloride.
Processes of imaging, especially xerographic imaging and printing, including digital, are also encompassed by the present invention. More specifically, the layered photoconductive imaging members of the present invention can be selected for a number of different known imaging and printing processes including, for example, electrophotographic imaging processes, especially xerographic imaging and printing processes wherein charged latent images are rendered visible with toner compositions of an appropriate charge polarity. Moreover, the imaging members of this invention are useful in color xerographic applications, particularly high-speed color copying and printing processes and which members are in embodiments, sensitive in the wavelength region of, for example, from about 500 to about 900 nanometers, and in particular from about 650 to about 850 nanometers, thus diode lasers can be selected as the light source.